Walter Koenig had a way to overlap his character with Worf's in The Next Generation

Way back in 1994, Walter Koenig had a brief conversation with the producers of Star Trek: The Next Generation about the possibility of a small part on the series. Though the cameo didn't happen, Koenig did appear on the first movie with The Next Generation crew—Star Trek: Generations. The part wasn't very big and didn't involve any interaction with Captain Picard or his crew. Koenig did have an idea of how to bring his character aboard the Enterprise that would have connected Chekov with Worf (Michael Dorn).

As everyone knows, Worf was raised by Russian parents, Helena and Sergey Rozhenko, after his Klingon parents were killed when he was very young. Being that Chekov was Russian, Koenig though that his character could have been friends with Worf's Russian grandparents. Worf might not have met Chekov when he was a child, but, if Koenig had been able to appear on The Next Generation, Worf could have contracted an illness that caused hallucinations. That would have enabled him to meet the man his grandparents befriended.

"When I learned that Worf in fact had Russian grandparents, I constructed a back story that would have involved Worf and Chekov meeting. I'm a little hazy now, but it was Worf on the ship, he becomes infected with something, and he begins having visions, hallucinatory episodes, and that's how I was able to introduce Chekov into the story."

- Walter Koenig

The part Koenig envisioned could have been something similar to how George Takei and Grace Lee Whitney appeared in Star Trek: Voyager's third season episode, "Flashback." Because of mind melds, Tuvok (Tim Russ) flashed back to his time aboard the USS Excelsior when he was serving under Captain Sulu. This gave Takei and Whitney more than just cameo appearances.

Koenig did make a voice appearance in the final season of Star Trek: Picard as President Anton Chekov, but his character has not returned to Star Trek otherwise. With the prospect of William Shatner returning as Captain Kirk thanks to de-aging technology, the same could happen with Koenig. In fact, a Trek series or movie could put the two of them together again for a great nod to the fans.